Hydrofluorocarbons, HFC's, are of great interest due to their potential to replace ozone-depleting chlorofluorocarbons, CFC's, and hydrochlorofluorocarbons, HCFC's. For example, an azeotropic mixture of difluoromethane ("HFC-32") and pentafluoroethane ("HFC-125") has been identified as a replacement for chlorodifluoromethane ("HCFC-22") in refrigeration and air-conditioning applications. Binary mixtures of HFC-32 and 1,1,1,2-tetrafluoroethane ("HFC-134a") and ternary mixtures of HFC-32, HFC-134a, and HFC-125 also have been proposed as HCFC-22 replacements.
Methods for the production of HFC's, such as HFC-32, are known. For example, U.S. Pat. No. 5,426,252 discloses a catalytic hydrodechlorination process in which HCFC-22 and dichlorodifluoromethane ("CFC-12") are reacted with hydrogen in the presence of a palladium-based catalyst to produce HFC-32. This process is disadvantageous in that it both requires formation of the feed materials from the corresponding chlorocarbons and has low conversion and poor selectivity in the hydrogenation step.
Another method is exemplified in U.S. Pat. Nos. 5,446,215 and 5,463,139, which disclose the reaction of formaldehyde and hydrogen fluoride in the presence of a solvent to produce bis(fluoromethyl ether) which is then dehydrated to yield HFC-32. The multiple steps of this process and its requirement of intermediate purification makes this method economically disadvantageous.
U.S. Pat. No. 5,495,057 discloses the liquid phase preparation of HFC-32 from HCC-30, hydrogen fluoride and antimony pentachloride at 70.degree. C. to 90.degree. C. and 11 to 12 kg/cm.sup.2 pressure. This process is disadvantageous because the use of antimony pentahalide catalyst and a hydrogen fluoride system is extremely corrosive to most metals and often, the antimony pentahalide is reduced to less active antimony trihalide in the fluorination reactions.
Thus, a need exists for an efficient and economical process for the fluorination of hydrohalomethanes, including HCC-30.